Process to remove sulfur using zinc containing sorbent subjected to steam treatment

ABSTRACT

A sorbent composition is provided comprising: (a) a zinc component; (b) a colloidal oxide component; and (c) a metal oxide component. This sorbent composition can be subjected to a steaming treatment that improves its sulfur loading capability.

This application is a Division of application Ser. No. 08/483,358, nowU.S. Pat. No. 5,726,117, filed on Jun. 7, 1995.

BACKGROUND

This invention relates to the field of sorbent compositions.

The removal of sulfur from fluid streams has long been desirable, aswell as necessary, for a variety of reasons. If asulfur-containing-fluid-stream is to be released as a waste stream,removal of such sulfur from the fluid stream is often necessary to meetcertain environmental regulations. If a sulfur-containing-fluid-streamis to be used in a catalytic process, removal of such sulfur is oftennecessary to prevent catalyst poisoning.

During sulfur removal processes these sorbents eventually become soloaded with sulfur that their ability to remove sulfur from asulfur-containing-fluid-stream is greatly diminished. Consequently,these sorbents arc subjected to a regeneration process that regeneratesthe sorbent. However, the gases used to regenerate these sulfur-loadedsorbents usually contain steam. This steam can greatly decrease theeffectiveness of such sorbents in their sulfur removing capabilities.

SUMMARY

It is an object of this invention to provide a sorbent composition.

It is another object of this invention to provide a sorbent compositionthat has been subjected to a steaming treatment.

It is another object of this invention to provide a process to make asorbent composition.

It is another object of this invention to provide a process to use asorbent composition.

In accordance with this invention a sorbent composition is providedcomprising: (a) a zinc component; (b) a colloidal oxide component; and(c) a metal oxide component.

In accordance with this invention a sorbent composition is providedcomprising: (a) a zinc component; (b) a colloidal oxide component; and(c) a metal oxide component; wherein said sorbent composition issubjected to a steaming treatment.

In accordance with this invention a process is provided comprising: (a)contacting a zinc component, a colloidal oxide component, and a metaloxide component, together; and then (b) subjecting the compositionproduced in (a) to a steaming treatment where said steaming treatment isconducted at a temperature in the range of about 100° to about 1100° C.

In accordance with this invention a process is provided to remove sulfurfrom a sulfur containing fluid stream. This process comprises contactingsaid sulfur-containing-fluid-stream with a composition comprising a zinccomponent, a colloidal oxide component, and a metal oxide component.

DETAILED DESCRIPTION OF THE INVENTION

Sorbent compositions of this invention comprise (or optionally, consistessentially of, or consist of) a zinc component, a colloidal oxidecomponent, and a metal oxide component.

Generally, the zinc component is zinc oxide. However, it may be acompound that is convertible to zinc oxide under the conditions ofpreparation described herein. Examples of such compounds include, butare not limited to, zinc sulfide, zinc sulfate, zinc hydroxide, zinccarbonate, zinc acetate, and zinc nitrate. The amount of the zinccomponent present in the sorbent composition is in the range of about 10to about 90 weight percent based on the total weight of the sorbentcomposition. However, an amount in the range of about 25 to about 75weight percent is preferred and an amount in the range of about 40 toabout 60 weight percent is most preferred.

The colloidal oxide component is generally a liquid medium comprisingfinely divided, colloidal-sized particles of a metal oxide. Theseparticles are, in general, homogeneously distributed throughout theliquid medium. The size of these particles varies, but in general, thesize of these particles is in the range of about 10 to about 10,000angstroms. Typical solid concentrations in such colloidal oxidecomponents can range from about 1 to about 30 weight percent based onthe total weight of the colloidal oxide component. The pH of thecolloidal oxide component can range from about 2 to about 11 dependingon the method of preparation of the colloidal oxide component. Inanother embodiment, the colloidal oxide can be a solid comprisingparticles of a metal oxide. For example, the colloidal oxide can be apowder comprising particles of a metal oxide. However, when thecolloidal oxide is a solid comprising particles of a metal oxide, itshould have the ability to be readily dispersed in a liquid medium. Inother words, if the colloidal oxide component is a solid comprisingparticles of a metal oxide, then under the conditions of preparationdescribed herein, the colloidal oxide should be able to form adispersion that contains colloidal-size particles. The metal oxide, in apreferred embodiment, is selected from the group consisting of alumina,silica, titania, zirconia, tin oxide, antimony oxide, cerium oxide,yttrium oxide, copper oxide, iron oxide, manganese oxide, molybdenumoxide, tungsten oxide, chromium oxide, and mixtures of two or morethereof. Currently, in a more preferred embodiment, the colloidal oxidecomponent comprises colloidal alumina, colloidal silica, or mixturesthereof. The amount of metal oxide present in the sorbent compositionfrom the colloidal oxide component is in the range of about 1 to about30 weight percent based on the total weight of the sorbent composition.However, an amount in the range of about 1 to about 20 weight percent ispreferred and an amount in the range of about 5 to about 15 weightpercent is most preferred.

The metal oxide component can be a metal silicate, a metal aluminate, ametal aluminosilicate, or a mixture thereof. The metal in the metaloxide component can be selected from the group consisting of beryllium,magnesium, calcium, strontium, barium, radium, zinc, cadmium, mercury,and mixtures thereof. However, magnesium, calcium, zinc and mixturesthereof are more preferred, and zinc is most preferred. Examples of suchmetal oxide components include, but are not limited to, magnesiumsilicate, calcium silicate, dicalcium silicate, zinc silicate, calciumaluminate, and zinc aluminate. The amount of the metal oxide componentpresent in the sorbent composition is in the range of about 5 to about90 weight percent based on the total weight of the sorbent composition.However, an amount in the range of about 10 to about 75 weight percentis preferred and an amount in the range of about 15 to about 60 weightpercent is most preferred. In another embodiment, the metal oxidecomponent can be formed in-situ during the preparation of the sorbentcomposition. For example, zinc oxide and silica can be contactedtogether during the preparation of the sorbent and subjected to athermal and\or hydrothermal treatment thereby forming a metal oxidecomponent that comprises zinc silicate.

The above three components can be contacted together in any manner knownin the art. Additionally, they can be contacted in any order. Thecomponents, after initially contacting them together, can beagglomerated by any manner known in the art. This agglomeration caninclude a sizing step where a desired particle size distribution can beobtained. Additionally, such sizing operations can be conducted afterany drying or calcining operation.

Usually, after the components are agglomerated, they are subjected to adrying step. This drying step is generally used to remove the liquidmedium of the colloidal oxide component. The drying step can beconducted at any temperature suitable for removing substantially all ofthe liquid medium. These temperatures are generally in the range ofabout 50° to about 300° C. However, it is more preferred if thetemperature is in the range of about 100° to about 200° C. Drying timesdepend upon the liquid medium and the drying temperature, but ingeneral, drying times of about 0.5 to about 4 hours are preferred.

The dried composition can then be calcined to form a calcinedcomposition. The calcination can be conducted under any suitableconditions that remove residual water, oxidize any combustibles and\orform a metal oxide component. The dried composition can be calcined inan oxygen containing ambient. Generally, the temperature that thecalcination takes place at is in the range of about 300° to about 1300°C. However, it is more preferred if the temperature is in the range ofabout 450° to about 1100° C. The calcination should be conducted for aperiod of time in the range of about 0.5 to about 24 hours. Generally,any zinc component that is not in the form of zinc oxide can beconverted to zinc oxide at this point of the preparation. Furthermore,zinc oxide and silica can be combined to form zinc silicate at thispoint of the preparation.

It is sometimes desirable to have the sorbent composition include aGroup VIII metal oxide promoter. These promoters can improve thephysical and chemical properties of the sorbent composition. Forexample, these Group VIII metal oxide promoters can increase the abilityof the sorbent composition to hydrogenate sulfur oxide to hydrogensulfide. Furthermore, such promoters can increase the ability of thesorbent composition to regenerate after becoming spent in a sulfurremoval process. Examples of suitable Group VIII metal oxide promotersinclude, but are not limited to, iron oxide, cobalt oxide, nickel oxide,ruthenium oxide, rhodium oxide, palladium oxide, osmium oxide, iridiumoxide, and platinum oxide. The amount of promoter in the sorbentcomposition is in the range of about 0.1 to about 20 weight percentbased on the weight of the sorbent composition. However, it is morepreferable if the amount is in the range of about 1 to about 15 weightpercent, and most preferably the amount is in the range of about 5 toabout 10 weight percent.

The promoter can be added to the sorbent composition in the form of theelemental metal, metal oxide, and\or metal-containing compounds that areconvertible to metal oxides under the calcining conditions describedherein. Some examples of such metal-containing compounds include metalacetates, metal carbonates, metal nitrates, metal sulfates, metalthiocyanates and mixtures of any two or more thereof.

The elemental metal, metal oxide, and\or metal-containing compounds canbe added to the sorbent composition by any method known in the art. Onesuch method is the impregnation of the sorbent composition with asolution, either aqueous or organic, that contains the elemental metal,metal oxide, and\or metal-containing compounds. After the elementalmetal, metal oxide, and\or metal-containing compounds have been added tothe sorbent composition, the promoted composition is dried and calcined,as described hereinafter.

The elemental metal, metal oxide, and\or metal-containing compounds canbe added to the sorbent composition as components of the originalmixture, or they can be added after the sorbent composition has beendried and calcined. If the metal oxide promoter is added to the sorbentcomposition after it has been dried and calcined, then the now-promotedcomposition is dried and calcined a second time. The now-promotedcomposition is preferably dried at a temperature in the range of about50° to about 300° C., but more preferably, the drying temperature willrange from about 100° to about 250° C., for a period of time in therange of about 0.5 to about 8 hours, more preferably in the range ofabout 1 to about 5 hours. The dried, promoted composition is thencalcined in the presence of oxygen or an oxygen-containing gas at atemperature in the range of about 300° to about 800° C., and morepreferably in the range of from about 450° to about 750° C., untilvolatile matter is removed and until at least a portion of the elementalmetal and\or the metal-containing compounds is converted to a metaloxide. The time required for this calcining step will generally be inthe range of about 0.5 to about 4 hours, and will preferably be in therange of from about 1 to about 3 hours.

In another embodiment of this invention, the sorbent composition issubjected to a steaming treatment. This steaming treatment comprisescontacting the sorbent composition with a steam mixture that compriseswater and air. If desired, this mixture can contain other gases such as,for example, nitrogen, helium, and argon. The steam mixture shouldcontain about 5 to about 90 volume percent water, the remaindercomprising air. Preferably, the steam mixture should contain about 10 to80 volume percent water, the remainder comprising air. The steamingtreatment should be conducted at a temperature in the range of about100° to about 1100° C. However, it is preferred if the steamingtreatment is conducted at a temperature in the range of about 200° toabout 900° C. Generally, the amount of time that the steam mixture iscontacted with the sorbent composition will depend on the temperaturethe steaming treatment is conducted at. However, the amount of time thatthe steam mixture is contacted with the sorbent composition is fromabout 1 to about 24 hours and preferably from about 2 to about 8 hours.The steam treatment can take place either before, or after,incorporating a Group VIII metal oxide promoter. Additionally, one ormore steaming treatments can be conducted to obtain a desired sorbentcomposition. Furthermore, the sorbent composition to be subjected to thesteaming treatment can be in the form of a dry powder that is contactedwith the steam mixture, or it can be in the form of a water containingsorbent composition that is subjected to the above-identifiedtemperatures.

The sorbent compositions of this invention can be used in sulfur removalprocesses where there is achieved a contacting of the sorbentcomposition with a sulfur-containing gaseous feed stream, andthereafter, of the sorbent composition with oxygen or anoxygen-containing gas, which is utilized to regenerate the sorbentcomposition. The sulfur removal process is in no way limited to the useof a particular apparatus. The sulfur removal process can be carried outusing a fixed bed of sorbent composition, a fluidized bed of sorbentcomposition, or a moving bed of sorbent composition. Examples of suchsulfur removal processes are disclosed in U.S. Pat. Nos. 4,990,318;5,077,261; 5,102,854; 5,108,975; 5,130,288; 5,174,919; 5,177,050;5,219,542; 5,244,641; 5,248,481; and 5,281445; the disclosures of whichare hereby incorporated by reference. The sorbent compositions of thisinvention are useful in sulfur removal processes that are conducted attemperatures from about 300° to about 800° C. Additionally, they areespecially useful in sulfur removal processes that are conducted attemperatures greater than about 430° C. but less than about 650° C.Furthermore, the sorbent compositions of this invention are especiallyuseful in sulfur removal processes that are conducted at temperatures inthe range of about 475° C. to about 625° C.

EXAMPLES

These examples are provided to illustrate the invention. The particularreactants, conditions, and the like, are meant to be illustrative of theinvention and are not meant to be construed as limiting the invention.

EXAMPLE ONE

Sorbent Preparation

A sorbent was prepared by dry mixing 158.9 grams of Micro-Cel T-38calcium silicate (Celite Corporation, Lompoc, Calif.) and 198.6 grams ofpowdered zinc oxide for 10 minutes in a mix-muller. This composition wasthen spray impregnated with 197.0 grams of Nyacol Al-20 alumina in 140grams of deionized water. The resulting material was further mixed foran additional 35 minutes. The resulting wet paste was agglomerated bydrying at 150° C. for three hours and calcining at 635° C. for one hour.The dried agglomerates were granulated in a bench top granulator fittedwith a 50 mesh screen (Stokes Pennwalt, Warminster, Pa., Model 43Granulator). Two hundred fifty grams of the granulated material wasplaced in a rotating mixer and impregnated with 74.27 grams of nickelnitrate dissolved in 135.3 grams of deionized water. This was then driedat 150° C. for one hour and calcined at 635° C. for one hour. Theproduct was screened to remove particles larger than 50 mesh and smallerthan 200 mesh. Two hundred fifty grams of the screened product wassubjected to a second nickel impregnation using 24.75 grams of nickelnitrate in 122.5 grams of deionized water. This material was dried at121° C. overnight. The dried product was designated "Sorbent A."

Twenty grams of Sorbent A was placed in a quartz tube and exposed to amixture of 8.0 cc/hr deionized water, 2500 cc/hr air and 7500 cc/hrnitrogen for 24 hours at 760° C. The resulting material was designated"Sorbent B."

A comparison composition was prepared as follows. Twenty pounds ofCelite® powder was placed in a mix muller. While mixing, the Celite®powder was spray impregnated over a period of six to eight minutes with24.4 pounds of Nyacol Al-20 colloidal alumina using a pump and spraynozzle. To this was added, in small increments, 25.0 pounds of zincoxide, with mixing for 22-24 minutes. As needed, the sides, blades andwheels of the mixer were scraped to ensure a homogeneous mix. The totalmix time including alumina addition did not exceed thirty minutes. Themoisture content of the mix was between 26-27%. The mix had a moist,powdery appearance at this point. The mix was then extruded using ascrew extruder with water-cooled barrel controlled at 45°-50° C. Theextrudate was dried on trays in an air circulating oven at 150° C. forthree hours. The dried extrudate was calcined at 635° C. for one hourusing a belt calciner. Nickel was then spray impregnated onto thecalcined base in a coater using nickel(II) nitrate dissolved in water.The aqueous nickel solution used was prepared by dissolving 134.7 gramsof nickel(II) nitrate hexahydrate per pound of calcined base insufficient water to effect an 85% incipient wetness impregnation. Afterimpregnation, the material was dried at 150° C. for three hours andcalcined at 635° C. for one hour. The resulting material was designated"Sorbent C."

A portion of Sorbent C was treated with steam in a quartz tube in amanner analogous to the treatment described above for Sorbent A. Theresulting material was designated "Sorbent D."

Sulfur Removal From Gases

In this test, sorbents are alternately contacted at 427°-649° C. withhydrogen sulfide diluted with gases such as carbon dioxide and nitrogen,and at 593°-649° C. with air. During the contact with hydrogen sulfide,the sulfur loading on the sorbent was determined to be complete whenhydrogen sulfide was detected at 100 ppm in the effluent. At this point,the regeneration by contact with air was begun. The results are given inTable I.

                  TABLE I                                                         ______________________________________                                        Sulfur Loading Study Results                                                  Temperature, °C.                                                                      Cycle  Sulfur Loading, %                                       ______________________________________                                        Sorbent A                                                                     427            1      3.0                                                     427            2      3.7                                                     427            3      3.1                                                     538            4      9.3                                                     538            5      10.8                                                    538            6      12.7                                                    649            7      16.3                                                    649            8      15.4                                                    427            9      7.0                                                     427            10     9.1                                                     427            11     10.0                                                    Sorbent B                                                                     427            1      1.1                                                     427            2      2.1                                                     427            3      2.6                                                     427            4      2.8                                                     427            5      3.1                                                     427            6      3.2                                                     649            7      15.1                                                    649            8      16.5                                                    649            9      16.1                                                    593            10     14.0                                                    593            11     13.2                                                    593            12     14.9                                                    538            13     13.7                                                    538            14     15.4                                                    538            15     15.6                                                    Sorbent C                                                                     427            1      12.4                                                    427            2      14.2                                                    427            3      14.3                                                    427            4      13.7                                                    427            5      13.7                                                    427            6      13.7                                                    427            7      13.8                                                    427            8      13.5                                                    427            9      13.3                                                    427            10     13.5                                                    427            11     13.5                                                    427            12     13.5                                                    427            13     13.3                                                    427            14     13.3                                                    427            15     13.7                                                    427            16     13.0                                                    Sorbent D*                                                                    427            1      12.8                                                    427            2      15.2                                                    427            3      14.3                                                    427            4      --                                                      427            5      4.2                                                     538            6      2.9                                                     538            7      8.5                                                     538            8      6.4                                                     538            9      6.5                                                     538            10     5.8                                                     538            11     5.5                                                     ______________________________________                                         *For Sorbent D, for cycles 3-11, the regeneration gas also contained          steam.                                                                   

A comparison of the data for Sorbents A and B shows that the latter hassuperior sulfur loading at temperatures greater than about 430° C. butless than about 650° C., indicating a beneficial effect of the steamtreatment it received. A comparison of the data for Sorbents C and Dshows that the comparison material is similar in behavior when steam isnot present in the regeneration gases. However, when steam is includedin the regeneration gases for Sorbent D, its sulfur loading decreasedsignificantly.

EXAMPLE TWO

In this example, an inventive preparation is conducted in a manner toproduce an inventive sorbent in which the active ingredient, zinc oxide,and the promoter, nickel oxide, are supported in an in-situ formedmatrix comprising zinc silicate.

The sorbent was prepared by dry mixing in a mix-muller 1584 grams zincoxide and 216 grams Celite® silica for 5 minutes. The resulting powderwas spray-impregnated with a solution of 250 grams Vista Dispal aluminain 450 grams of deionized water. The resulting wet paste wasagglomerated by drying at 150° C. for 3 hours and calcining at 635° C.for one hour. The dried material was granulated in a bench top StokesPennwalt Granulator (Model 43, Stokes Penwalt, Warminster, Pa.) fittedwith a 50 mesh screen. One hundred fifty-one grams of the -20 to +140mesh fraction was placed in a quartz reactor and steamed with a mixtureof 1.0 cc/min deionized water and 336 cc/min air at 870° C. for 20hours. One hundred twenty-five grams of the steamed material was thenplaced in a rotating mixer and impregnated with 37.1 grams of nickelnitrate dissolved in 26.6 grams of deionized water. This material wasthen dried at 150° C. for one hour and calcined at 635° C. for one hour.The resulting material was designated "Sorbent E." An X-ray diffractionanalysis indicated that there was about 22.1 weight percent zincsilicate in the sorbent composition together with zinc oxide and nickeloxide. It is estimated that the sorbent composition also contain someunreacted silica, as well as, the alumina.

Sorbent E was tested for sulfur removal from gases as was indicatedpreviously for Sorbents A-D. The results are given in Table II.

                  TABLE II                                                        ______________________________________                                        Results with Sorbent E**                                                      Temperature, °C.                                                                      Cycle  Sulfur Loading, %                                       ______________________________________                                        538            1      22.4                                                    538            2      24.4                                                    538            3      24.0                                                    538            4      23.9                                                    538            5      31.9                                                    538            6      27.4                                                    538            7      24.8                                                    538            8      24.8                                                    538            9      24.1                                                    538            10     24.0                                                    538            11     23.7                                                    538            12     23.2                                                    538            13     22.4                                                    538            14     24.1                                                    538            15     22.8                                                    538            16     21.3                                                    538            17     19.2                                                    538            18     16.5                                                    538            19     17.3                                                    538            20     18.5                                                    538            21     18.0                                                    538            22     16.9                                                    ______________________________________                                         **For Sorbent E, for cycles 2-22, the regeneration gas also contained         steam.                                                                   

The data presented in Table II show that Sorbent E is also effective insulfur removal from gases at high temperatures and under moistconditions. This is in contrast to the severely decreased sulfur loadingof Sorbent D when tested under moist conditions. It is noted that whilethe level of active zinc in Sorbent E is calculated to be 57.5 weightpercent vs. 46.6 weight percent for Sorbent D, the 23.4% higher activezinc level of Sorbent E is insufficient to account for the>400% higherlevel of sulfur loading of Sorbent E after an equivalent number ofregeneration cycles with steam (compare cycle 11 of Sorbent D with cycle12 of Sorbent E, both after nine cycles with steam).

We claim:
 1. A process to remove sulfur from a sulfur containing fluidstream said process comprising contacting said sulfur containing fluidstream with a sorbent composition comprising a zinc component, acolloidal oxide component, and a metal oxide component wherein saidsorbent composition has been subjected to a temperature in the range ofabout 50° C. to about 800° C. to remove substantially all of the liquidmedium, and wherein said sorbent composition is then subjected to asteaming treatment that comprises contacting said sorbent compositionwith a steam mixture that comprises water and air.
 2. A processaccording to claim 1 wherein said steam mixture contains about 5 toabout 90 volume percent water.
 3. A process according to claim 2 whereinsaid steaming treatment is conducted at a temperature in the range ofabout 100° C. to about 1100° C.
 4. A process according to claim 3wherein said zinc component is present in said sorbent composition in anamount from about 25 to about 75 weight percent.
 5. A process accordingto claim 4 wherein said zinc component is present in said sorbentcomposition in an amount from about 40 to about 60 weight percent.
 6. Aprocess according to claim 5 wherein said colloidal oxide component hasa metal oxide selected from the group consisting of alumina, silica,titania, zirconia, tin oxide, antimony oxide, cerium oxide, yttriumoxide, copper oxide, iron oxide, manganese oxide, molybdenum oxide,tungsten oxide, chromium oxide, and mixtures thereof.
 7. A processaccording to claim 6 wherein said colloidal oxide component is used in aquantity that presents an amount of metal oxide in said sorbentcomposition from about 1 to about 20 weight percent based on the weightof said sorbent composition.
 8. A process according to claim 7 whereinsaid colloidal oxide component is used in a quantity that presents anamount of metal oxide in said sorbent composition from about 5 to about15 weight percent based on the weight of said sorbent composition.
 9. Aprocess according to claim 8 wherein said metal oxide component containsa metal selected from the group consisting of magnesium, calcium, zincand mixtures thereof.
 10. A process according to claim 9 wherein theamount of metal oxide component is present in said sorbent compositionin an amount in the range of about 10 to about 75 weight percent basedon the weight of said sorbent composition.
 11. A process according toclaim 1 where said sorbent composition further comprises a Group VIIImetal oxide promoter.
 12. A process according to claim 11 wherein saidGroup VIII metal oxide promoter is present in said sorbent compositionin an amount in the range of about 1 to about 15 weight percent based onthe weight of said sorbent composition.
 13. A process according to claim12 wherein said steam mixture contains about 5 to about 90 volumepercent water.
 14. A process according to claim 13 wherein said steamingtreatment is conducted at a temperature in the range of about 100° C. toabout 1100° C.
 15. A process according to claim 14 wherein said zinccomponent is present in said sorbent composition in an amount from about25 to about 75 weight percent.
 16. A process according to claim 15wherein said zinc component is present in said sorbent composition in anamount from about 40 to about 60 weight percent.
 17. A process accordingto claim 16 wherein said colloidal oxide component has a metal oxideselected from the group consisting of alumina, silica, titania,zirconia, tin oxide, antimony oxide, cerium oxide, yttrium oxide, copperoxide, iron oxide, manganese oxide, molybdenum oxide, tungsten oxide,chromium oxide, and mixtures thereof.
 18. A process according to claim17 wherein said colloidal oxide component is used in a quantity thatpresents an amount of metal oxide in said sorbent composition from about1 to about 20 weight percent based on the weight of said sorbentcomposition.
 19. A process according to claim 18 wherein said colloidaloxide component is used in a quantity that presents an amount of metaloxide in said sorbent composition from about 5 to about 15 weightpercent based on the weight of said sorbent composition.
 20. A processaccording to claim 19 wherein said metal oxide component contains ametal selected from the group consisting of magnesium, calcium, zinc andmixtures thereof.
 21. A process according to claim 20 wherein the amountof metal oxide component is present in said sorbent composition in anamount in the range of about 10 to about 75 weight percent based on theweight of said sorbent composition.
 22. A process according to claim 21wherein said Group VIII metal oxide promoter is selected from the groupconsisting of cobalt oxide and nickel oxide.